Four operating parameters of supercritical carbon dioxide extraction were optimized by the response surface method. The central composite rotatable design was used to maximize extraction recovery of essential oil (specifically diosgenin) from Tribulus terrestris. The obtained data were adequately fitted into two second-order polynomial models for essential oil and diosgenin. The linear terms of pressure, temperature, and extraction dynamic time, the quadratics of pressure and extraction dynamic time, and the interactions of the following two variables: (i) pressure and temperature, (ii) pressure and extraction dynamic time, and (iii) temperature and extraction dynamic time had significant effects on diosgenin recovery.

in Wiley Online Library (wileyonlinelibrary.com).Supercritical carbon dioxide (CO 2 ) effective extraction parameters (pressure, temperature, static extraction time, and dynamic extraction time) of oil recovery from evening primrose seeds were optimized via response surface methodology (RSM). The results of this study indicated that the linear terms of static and dynamic time and the quadratics of temperature and pressure, as well as the interactions of temperature and static time, pressure and temperature had a significant effect on the oil recovery. The optimum extraction conditions of 14.2 MPa, 47.3 C, 30 min (static extraction time) and 150 min (dynamic extraction time) were obtained. Applying the optimum conditions, a mean experimental recovery of 92.98% (triplicate experiment) was achieved, which is well compatible with the RSM-predicted value (93.61%). The fatty acid composition of extracted evening primrose oil using supercritical CO 2 was compared with that obtained by Soxhlet method in which minor difference was observed.

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